I modified the Small Dice Tower by scaling it down to 80% of original size and changing the opening to have a pointed arch. This removes the need for any supports to print the opening. I also scaled down the ramps slightly to make sure they slide through the slots even when the slots print messily (as they tend to do due to their angle).
Update: I've added a funnel for the more enthusiastic dice throwers out there. The funnel sits on top and can be printed separately. It needs no supports and can be printed at 100% infill as it is just a thin shell. Funnel inspired by Buchnerb's remix here: http://www.thingiverse.com/thing:1365529
Update 2: The latest file (tower_and_funnel_combined.stl) has the funnel integrated into the tower model, and an improved ramp which prevents the dice from bouncing back out of the tray - keeping them at the front where they're easier to see. I recommend printing this version.
Print two of the ramps and slide them through the slots. You can glue them in place if they're loose.